Carrier Concentration Dependence of the Electrical Behaviors of ITO Contacts on n-Type ZnO

We report on the carrier concentration dependence of the electrical characteristics of ITO Ohmic contacts to unintentionally doped n-ZnO (Nd = 1.79×1016 -5.76× 1018 cm-3). For n-ZnO layers with carrier concentrations in excess of 8.04×1017 cm-3, as-deposited ITO contacts produce good Ohmic behavior. However, as-deposited ITO contacts to n-ZnO with carrier concentrations less than ~4×1017 cm-3 yield non-Ohmic behaviors. We show that when annealed at 400℃ in a nitrogen ambient, the ITO contacts to ZnO (with carrier concentrations exceeding 4.08×1017cm-3) become Ohmic with a specific contact resistivity in the range of 8.76×10-3 - 1.51× 10-4 Ω2. Based on carrier transportation theory, we describe the carrier concentration and the annealing temperature dependence of the carrier transport mechanisms KCI Citation Count: 0